A. Field of the Invention
The present invention relates generally to the fields of detection, diagnosis and treatment of human disease states and methods relating thereto. More particularly, the present invention concerns probes and methods useful in diagnosing, identifying and monitoring the progression of diseases of the prostate through measurements of gene products. Also disclosed are various diagnostic and therapeutic methods and screening assays using the compositions of the invention.
B. Description of the Related Art
Carcinoma of the prostate (PCA) is the second-most frequent cause of cancer related death in men in the United States (Boring et al., 1993; Wingo et. al., 1997). The increased incidence of prostate cancer during the last decade has established prostate cancer as the most prevalent of all cancers (Carter and Coffey, 1990). Although prostate cancer is the most common cancer found in United States men, (approximately 210,000 newly diagnosed cases/year), the molecular changes underlying its genesis and progression remain poorly understood (Boring et al., 1993). According to American Cancer Society estimates, the number of deaths from PCA is increasing in excess of 8% annually.
An unusual challenge presented by prostate cancer is that most prostate tumors do not represent life threatening conditions. Evidence from autopsies indicate that 11 million American men have prostate cancer (Dbom, 1983). These figures are consistent with prostate carcinoma having a protracted natural history in which relatively few tumors progress to clinical significance during the lifetime of the patient. If the cancer is well-differentiated, organ-confined and focal when detected, treatment does not extend the life expectancy of older patients.
Unfortunately, the relatively few prostate carcinomas that are progressive in nature are likely to have already metastasized by the time of clinical detection. Survival rates for individuals with metastatic prostate cancer are quite low. Between these two extremes are patients with prostate tumors that will metastasize but have not yet done so. For these patients, surgical removal of their prostates is curative and extends their life expectancy. Therefore, determination of which group a newly diagnosed patient falls within is critical in determining optimal treatment and patient survival.
Although clinical and pathologic stage and histological grading systems (e.g., Gleason's) have been used to indicate prognosis for groups of patients based on the degree of tumor differentiation or the type of glandular pattern (Carter and Coffey, 1989; Diamond et al., 1982; O'Dowd et al., 1997), these systems do not predict the progression rate of the cancer. While the use of computer-system image analysis of histologic sections of primary lesions for "nuclear roundness" has been suggested as an aide in the management of individual patients (Diamond et al., 1982), this method is of limited use in studying the progression of the disease.
Recent studies have identified several recurring genetic changes in prostate cancer including: allelic loss (particularly loss of chromosome 8p and 16q) (Bova. et al., 1993; Macoska et al, 1994; Carter et al, 1990), generalized DNA hypermethylation, (Isaacs et al., 1994), point mutations or deletions of the retinoblastoma (Rb) and p53 genes (Bookstein et al., 1990a; Bookstein et al., 1990b; Isaacs et al., 1991), alterations in the level of certain cell-cell adhesion molecules (i.e., E-cadherin/alpha-catenin)(Carter et al., 1990); Morton et al., 1993a; Morton et al., 1993b; Umbas et al., 1992), and aneuploidy and aneusomy of chromosomes detected by fluorescence in situ hybridization (FISH), particularly chromosomes 7 and 8 (Macoska et al., 1994; Visakorpi et al., 1994; Takahashi et al., 1994; Alcaraz et al., 1994).
The analysis of DNA content/ploidy using flow cytometry and FISH has been demonstrated to have utility predicting prostate cancer aggressiveness (Pearsons et al., 1993; Macoska et al., 1994; Visakorpi et al., 1994; Takahashi et al., 1994; Alcaraz et al., 1994; Pearsons et al., 1993; Veltri et al., 1994), but these methods are expensive, time-consuming, and the latter methodology requires the construction of centromere-specific probes for analysis.
Specific nuclear matrix proteins have been reported to be associated with prostate cancer. (Partin et al., 1993). However, these protein markers apparently do not distinguish between benign prostate hyperplasia and prostate cancer. (Partin et al., 1993). Unfortunately, markers which cannot distinguish between benign and malignant prostate tumors are of little value.
A recent development in this field was the identification of prostate metastasis suppresser genes, KAI1, E-cadherin, alpha-catenin and GST-pi (Dong et al., 1995; Carter et al., 1990; Morton et al., 1993a; Morton et al., 1993b; Umbas et al., 1992; Cookson et al., 1997; Lee et al., 1997). Insertion of wild-type KAI1 gene into a rat prostate cancer line caused a significant decrease in metastatic tumor formation (Dong et al., 1995). However, detection of KAI1, E-cadherin, alpha-catenin, and GST-pi mutations are dependent upon direct sampling of mutant prostate cells (Dong et al., 1996; Umbas et al, 1992; Cookson et al, 1997; Murray et al., 1995). Thus, either a primary prostate tumor must be sampled or else sufficient transformed cells must be present in blood, lymph nodes or other tissues to detect the missing or abnormal gene. Further, the presence of a deleted gene may frequently be masked by large numbers of untransformed cells that may be present in a given tissue sample.
The most commonly utilized current tests for prostate cancer are digital rectal examination (DRE) and analysis of serum prostate specific antigen (PSA). Although PSA has been widely used as a clinical marker of prostate cancer since 1988 (Partin and Oesterling, 1994), screening programs utilizing PSA alone or in combination with digital rectal examination have not been successful in improving the survival rate for men with prostate cancer (Partin and Oesterling, 1994). While PSA is specific to prostate tissue, it is produced by normal and benign as well as malignant prostatic epithelium, resulting in a high false-positive rate for prostate cancer detection (Partin and Oesterling, 1994).
Other markers that have been used for prostate cancer detection include prostatic acid phosphatase (PAP) and prostate secreted protein (PSP). PAP is secreted by prostate cells under hormonal control (Partin and Oesterling, 1994). It has less specificity and sensitivity than does PSA. As a result, it is used much less now, although PAP may still have some applications for monitoring metastatic patients that have failed primary treatments. In general, PSP is a more sensitive biomarker than PAP, but is not as sensitive as PSA (Huang et al., 1993). Like PSA, PSP levels are frequently elevated in patients with BPH as well as those with prostate cancer.
Another serum marker associated with prostate disease is prostate specific membrane antigen (PSMA) (Horoszewicz et al., 1987; Carter et al., 1996; Murphy et al., 1996). PSMA is a Type II cell membrane protein and has been identified as Folic Acid Hydrolase (FAH) (Carter et al., 1996). Antibodies against PSMA react with both normal prostate tissue and prostate cancer tissue (Horoszewicz et al., 1987). Murphy et al. (1995) used ELISA to detect serum PSMA in advanced prostate cancer. As a serum test, PSMA levels are a relatively poor indicator of prostate cancer. However, PSMA may have utility in certain circumstances. PSMA is expressed in metastatic prostate tumor capillary beds (Silver et al., 1997) and is reported to be more abundant in the blood of metastatic cancer patients (Murphy et al., 1996). PSMA messenger RNA (mRNA) is down-regulated 8-10 fold in the LNCaP prostate cancer cell line after exposure to 5-.alpha.-dihydroxytestosterone (DHT) (Israeli et al., 1994).
A relatively new potential biomarker for prostate cancer is human kallekrein 2 (HK2) (Piironen et al., 1996). HK2 is a member of the kallekrein family that is secreted by the prostate gland. In theory, serum concentrations of HK2 may be of utility in prostate cancer detection or diagnosis, but the usefulness of this marker is still being evaluated.
There remain, however, deficiencies in the art with respect to the identification of the genes linked with the progression of prostate diseases, including prostate cancer, and metastatic prostate cancer, the development of diagnostic methods to monitor disease progression, and the development of therapeutic methods and compositions to treat prostate diseases and cancers. The identification of genes which are differentially expressed in prostate diseases would be of considerable importance in the development of a rapid, inexpensive method to diagnose prostate diseases, including cancer. The identified genes would also be useful in therapeutic compositions, or in screening assays for therapeutic compounds.